Application Note
High Speed Infrared Imaging and the
Ballistics of “Punkin Chunkin”
In an effort to improve the performance of their massive 120 foot pneumatic air cannon at the 2012 World Punkin Chunkin
Championship (WCPC), American Chunker team captain Brian Labrie invited FLIR Systems’ infrared experts David Bursell
and Ron Lucier to join his diverse crew of chunkin’-crazed engineers, scientists, and fabricators. With the addition of a high
speed, high resolution MWIR infrared camera, the team was able to use thermal analysis of pumpkin ballistics to improve
design and performance as they prepared for the event.
Simply put, ballistics is the study of the flight, behavior, and effects of projectiles as well as the science or art of designing
and accelerating projectiles to achieve a desired performance. So, when you think about it, the science of launching a
pumpkin out of an oversized air cannon just to see how far it can go is a prime candidate for ballistic study.
By definition, a ballistic body moves and behaves freely, with changes in appearance, contour, or texture triggered
by ambient conditions, substances, or forces, i.e., the pressure of gases in a gun, rifling in a barrel, by gravity, by
temperature, or by air particles. In this case, the ballistic body in question just happens to be a large vegetable propelled
out of cannon by the force of released compressed air.
Background
The World Punkin Chunkin Championship
has taken place annually just after
Halloween in Sussex County, Delaware
for over 25 years. Over a hundred teams
compete in a number of divisions with the
air cannon contingent capable of hurling the
pumpkin by far the longest distances, over
4,000 feet for elite competitors, including
the American Chunker team.
If a giant cannon isn’t your thing, you can
also take in a variety of other wicked hurling
devices including catapults, torsion-powered
machines, trebuchets that operate with
counterweights, and for back-to-basics
types, even the simple force of brute human
strength. With the addition of female and
youth divisions, the contest is well on its way
to becoming an established sport—and a
popular televised holiday spectacle as well.
The Science Channel owns broadcast rights
to the event, airing the contest itself on
tape delay on Thanksgiving Day. “Road to the
Chunk” special segments are shown earlier to
pique viewer interest before the big day. The
Discovery Channel’s Mythbusters program
has also presented coverage of the event for
the last three years to stellar ratings
With profits from the event going primarily to a variety
of charity organizations, it’s mayhem and destruction
for a good cause
Panorama of pumpkin-hurling gadgets at the 2012 Chunk
How the Contest Works
Each division competes strictly for
distance except for the theatrical division
which relies on a fan vote. The teams get
three shots, one taken on each of three
consecutive days. Only the teams’ farthest
shot is scored for official results. Pumpkins
(by rule between 8-10 pounds and usually
thick-walled, robust varieties) must remain
whole after leaving the device for the chunk
to count. Pumpkins that burst after leaving
the barrel or sling are “pie” (short for
“pumpkin pie in the sky”).
Spotters riding on ATVs find the impact
point, and then a professional surveyor
calculates the distance based on GPS
coordinates of the impact and the machine.
The impact point is marked with colorcoded spray paint to avoid confusion with
future shots. Safety is a number one
priority with only fatality thus far being an
unfortunate duck felled by an air cannonlaunched pumpkin.
This thermal in the iron palette shows a pumpkin pieing” in
midflight—the area in the circle is not a cloud, but a trail of
exploding pumpkin matter.
Pumpkin Ballistics
As with any other air-powered projectile,
just how far Team AC’s pumpkin can fly
rests upon a number of variables which
lend themselves to thermal analysis.
These 3 images are part of a 10 shot stop motion sequence that show in very clear infrared detail exactly what happens
to the pumpkin as it reaches its final destination, a large chambered bucket, and distintegrates
• Are air leaks or moisture collecting inside
the cannon a factor?
• Exactly how does the pressurized air
strike the pumpkin?
• What is the speed of that air that propels
the pumpkin down the barrel?
• What is the barrel temperature?
• How much and in what manner does
barrel friction affect the pumpkin’s
speed?
• What is the impact of humidity and wind
speed on the pumpkin’s trajectory after it
exits the barrel?
• What is the pumpkin’s velocity?
• What can the spin or rotation tell us?
• What happens to the pumpkin as it
strikes the target?
The Next Victim
The SC6800’s highly sensitive cooled indium
antimonide (InSb) sensor detects even
subtle thermal differences and on-board
ambient drift compensation guarantees +/1% or 1 degree temperature measurement
accuracy of high speed targets or highly
dynamic thermal events in various thermal
environments.
Calibration Allows
Quantitative Analysis
The SC6800 on the job at Chunk 2012.
Why Use Infrared?
High-speed IR thermography can reveal
hidden features of fast-moving objects
when their temperature is higher than
the background. It takes a special kind of
camera to get this kind of data and the
infrared contingent on Team AC was able to
provide it via the FLIR SC6800.
Windowing Permits Stop
Motion Imagery
In order to capture the pumpkin’s flight,
fast frame rates were essential and this
camera offers 565 frames per second at
full 640 x 512 resolution. Windowing or
sampling of frames permits the capture of
thermal images at rates exceeding 10,000
frames per second. This is equivalent to
an exposure time of a few microseconds.
Thus, individual video frames can provide still
images of a fast-moving target or thermal
event, referred to as stop-motion imaging.
High Sensitivity and Accuracy
Avoid Blurring
Avoiding image blur is also tied to the
superior thermal sensitivity of FLIR camera
detectors. With highly sensitive detectors,
the data integration time can be shorter,
because less energy (IR radiation) is
required to record an acceptable image.
This is particularly important when you
need to see fast-moving, low-energy
targets like a pumpkin on a cool day, or
against a cool sky.
Slow Motion Video
Made Possible by Fast
Integration Times
Whether a stop-motion image or a video
sequence, high-speed IR cameras can
supply images of fast-moving objects with
minimal blur. FLIR’s advanced camera
systems make this possible with analog-todigital (A/D) converters that provide high
resolution and short integration times.
The shorter the integration time, the less
likely there will be blurring. When data
acquisition is fast enough, it’s possible to
capture a sequence and play it back in slow
motion. Check out the video featuring both
thermal and visible imagery of the 2012
Chunk on the FLIR website.
Stop motion IR image in iron palette of pumpkin in flight
In addition, the camera can be both
thermographically- and radiometricallycalibrated—meaning that it not only yields
fantastic imagery, but extremely high quality
data for quantitative analysis. The 50-500
continuous zoom lens ensures that even
from necessary safety distances, no detail
is lost. Full frame, full speed calibrated
imagery and data are output easily to
a data recorder for further analysis via
simultaneous gigabit Ethernet, Camera Link,
CoaxPress(CXP), or HD-SDI options.
The Results
At Chunk 2012, Team AC, only four years old, took home third place with a shot of 3,788.04 feet, just 93 feet out of first
place. For 2013, the American Chunkers have set goals to break the current world record (4,483 feet) and achieve a
major tournament win. Improvements have already enabled Team AC to chunk a pumpkin faster than the speed of sound.
Thermal imaging was used to check the validity of the speed gun mounted at the end of the cannon. Lines were drawn
every 10 feet on a building that the pumpkin passed by. By measuring how quickly the pumpkin reached these points,
speed could be very accurately measured.
BOSTON
This image shows the vapor/exhaust exiting the rear of the cannon after the shot. The triangular dark area within the
triangle is not a cold area on the building, but actually supersonic airflow—this pumpkin actually broke the sound barrier
(343.2 meters per second, roughly 768 miles per hour) complete with sonic boom. Without IR imaging, it is impossible to
even see the pumpkin leave the cannon with the naked eye, it’s moving so rapidly.
FLIR Systems, Inc.
9 Townsend West
Nashua, NH 03063
USA
PH:+1 866.477.3687
PH:+1 603.324.7611
PORTLAND
Corporate Headquarters
FLIR Systems, Inc.
27700 SW Parkway Avenue
Wilsonville, OR 97070
USA
PH:+1 877.773.3547
FX: +1 503.498.3153
www.FLIR.com/Thermography